During the non-menstrual period the dirt in the uterus, that is to say, the shed cells in the uterine cavity, will pass through the cervix and be discharged together with the cells shed from the cervical and vaginal mucosa to form leukorrhea. During menstruation the dirt in the uterine cavity, also known as shed endometrium, is expelled through the cervix as the uterus contracts. The normal size of the uterus is 7-8cm in length, 4-5cm in width and 2-3cm in thickness, and it can only hold 5ml of fluid, unless there is inflammation when the fluid oozes out, in which case it will increase and pass through the cervix to be expelled from the body. Normally, the cervical opening is closed, also to prevent the bacteria in the vagina upstream infection to the uterine cavity and lead to uterine infection. Women should also keep their vulva clean and hygienic, as both the vagina and cervix act as a barrier, and the uterine cavity is a sterile environment that does not lead to bacterial infections.